The present invention relates to an antenna device. In particular, the present invention relates to an antenna device in a microwave range and a millimeter wave range used for wireless communication and broadcast.
Heretofore, as an antenna for wireless communication or broadcast, there has been known a so-called parabola antenna for converging a radio wave to the focal point by means of a reflector such as one having a parabolic face. In order to set the parabola antenna, a column support having the thickness sufficient to obtain a sufficient strength, in consideration of the own weight of the antenna, wind, snow and so on, at the outside, e.g., the rooftop of an architectural structure such as a building, and a reflector is fixed to the column support, for example. Such antenna device is required to have durability so as to prevent the antenna or the support becoming rusty because the antenna device is exposed to rain water. However, the antenna device decays relatively fast and maintenance is necessary. Further, since the parabola antenna is set up at the outside, there is a problem of damaging the entire outer appearance of the architectural structure such as a building.
Accordingly, there have been considered that a parabola antenna or the like is set up in a room, or a lens or a diffraction grating is disposed at an opening of the building to converge the radio wave and increase energy density so that the radio wave is received. JP-A-11-150416 (concerning an antenna, Deutsche Telecom A.G.) proposes an antenna comprising a structure for diffracting electromagnetic signals in microwave and millimeter wave ranges, which is used instead of a window, or is integrally attached to a window or a part thereof. This publication proposes to attach a visually transparent diffraction structure (e.g., a Fresnel zone plate) or to unify it with a window.
JP-A-4-134909 discloses a diffracting ring type antenna comprising a diffraction ring having a transparent conductive thin film of high transparency formed on a window glass and a pickup antenna for receiving signals, which is disposed at or in the vicinity of the focal position of the diffraction ring. Further, the publication describes a technique that the diffraction ring made of the transparent conductive thin film is disposed on a transparent insulating plate and a one-piece body of the diffraction ring and the transparent insulating plate is attached to a window glass with an adhesive layer formed by coating an adhesive on a surface of the one-piece body.
However, when the antenna having the diffraction ring for converging the radio wave was attached to the window, there was a problem that a sufficient signal receiving performance could not be obtained due to loss caused by multipath reflection and so on caused between the diffraction ring and the window glass sheet. In particular, there was a problem that the multipath reflection and so on caused between the diffraction ring and the window glass sheet affected largely because of a short wavelength in the millimeter wave range or the microwave range.
It is an object of the present invention to eliminate the above-mentioned problems and to provide the invention described below.
(A) An antenna device which comprises a fitted member having transparency, a converging member for converging a radio wave, a space between the fitted member and the converging member, and a receiving portion for receiving the radio wave converged by the converging member and/or a transmitting portion for radiating a radio wave to the converging member.
(B) The antenna device described in the above-mentioned (A), wherein the fitted member is a window glass sheet fitted to a building; the converging member has a flat face, and the space is a space constituted by inclining relatively the converging member with respect to the window glass sheet.
(C) The antenna device described in the above-mentioned (A) or (B), wherein in a case that a receive power value is changed so as to take alternately a bottom value and a peak value depending on a change of the thickness of the space in the relation between the thickness of the space and the received power value, the thickness of the space is adjusted so that the received power value does not take a value in the vicinity of bottom values.
(D) The antenna device described in the above-mentioned (C), wherein in a case that the thickness of the fitted member satisfies the following formula (1) with respect to the wavelength of the radio wave and the incident angle of the radio wave, the space has an adjusted thickness:                                           (                                                                                2                    ⁢                    n                                    +                  1                                4                            -                              1                5                                      )                    ·                      λ            d                          ≤        L        ≤                              (                                                                                2                    ⁢                    n                                    +                  1                                4                            +                              1                5                                      )                    ·                      λ            d                                              (        1        )            
where n is an integer of 0 or more;
xcexd is a wavelength of the radio wave passing through the fitted member;       λ    d    =      λ                            ϵ          r                -                              sin            2                    ⁢          θ                    
(xcex is a wavelength of the radio wave in vacuum, xcex5d is the relative permittivity of the fitted member, and xcex8 is an incident angle of the radio wave), and L is a thickness of the fitted member.
(E) An antenna device which comprises a flat fitted member having transparency, an antenna member for transmitting a radio wave and/or receiving a radio wave and a space between the fitted member and the antenna member wherein in a case that a received power value is changed so as to take alternately a bottom value and a peak value depending on a change of the thickness of the space in the relation between the thickness of the space and the received power value in the antenna member, the thickness of the space is adjusted and determined so that the received power value does not take a value in the vicinity of bottom values.
Here, the antenna member includes the converging member for converging a radio wave and the transmitting portion and/or the receiving portion which transmits and/or receives a radio wave in the same manner as the antenna device described in the above-mentioned (A).
(F) The antenna device described in the above-mentioned (E), wherein in a case that the thickness of the fitted member satisfies the following formula (2) with respect to the wavelength of the radio wave and the incident angle of the radio wave, the space has an adjusted thickness:                                           (                                                                                2                    ⁢                    n                                    +                  1                                4                            -                              1                5                                      )                    ·                      λ            d                          ≤        L        ≤                              (                                                                                2                    ⁢                    n                                    +                  1                                4                            +                              1                5                                      )                    ·                      λ            d                                              (        2        )            
where n is an integer of 0 or more;
xcexd is a wavelength of the radio wave passing through the fitted member;       λ    d    =      λ                            ϵ          r                -                              sin            2                    ⁢          θ                    
(xcex is a wavelength of the radio wave in vacuum, xcex5r is the relative permittivity of the fitted member, and xcex8 is an incident angle of the radio wave), and L is a thickness of the fitted member.
(G) A method for arranging in substantially parallel a converging member for converging a radio wave closely to a fitted member wherein in a case that a received power value is changed so as to take alternately a bottom value and a peak value in the relation between the received power value and the thickness of a space between the converging member and the fitted member such as a window glass sheet, the thickness of the space is adjusted so that the received power value does not take a value in the vicinity of bottom values.
(H) A method for arranging in substantially parallel an antenna member closely to a fitted member such as a window glass sheet or the like in the construction of an antenna device wherein in a case that a received power value is changed so as to take alternately a bottom value and a peak value in the relation between the thickness of a space between the antenna member and the fitted member and the received power value, the thickness of the space is adjusted and determined so that the received power value does not take a value in the vicinity of bottom values. In particular, the method for arranging an antenna member wherein in a case that the thickness of the fitted member satisfies the above-mentioned formula (2), the thickness of the space is adjusted under determination.
(I) The antenna device or the method for arranging the same described in any one of the above-mentioned (A) to (H) wherein the radio wave is a radio wave in a microwave range or a millimeter wave range. Here, the microwave means a radio wave having a frequency of about 1 GHz-3 THz, and the millimeter wave means a radio wave having a frequency of about 30 GHz-300 GHz. The millimeter wave constitutes a part of the microwave band.
(J) The antenna device or the method for arranging the same described in any one of the above-mentioned (A) to (I) wherein the converging member is to converge, diffract, amplify or deflect the radio wave.
(K) The antenna device or the method for arranging the same described in any one of the above-mentioned (A) to (J) wherein the converging member is a Fresnel zone plate.
(L) With respect to the antenna device described in any one of the above-mentioned (A) to (K) in this specification, the function of receiving a radio wave is mainly described. However, the antenna device according to the present invention may be an antenna device for transmitting the radio wave in a predetermined direction by utilizing reversibility of transmitting/receiving the radio wave so that the radio wave radiated from a transmitting portion is diffracted or deflected to form a plane wave. Further, the above-mentioned formula (1) is the same as the above-mentioned formula (2). Accordingly, the formula (1) is used as a representative example.